1. Field of the Invention
The invention relates to counterbalanced pumps and more particularly to improvements in the operation thereof.
2. Description of the Prior Art
In my prior U.S. patent applications Ser. Nos. 824,346 and 933,269, now U.S. Pat. Nos. 4,179,947 and 4,197,766, respectively, I have described a counterbalanced pump for use on oil wells wherein sheave or roller chains are spirally wound around mandrels connected for common rotation and as one chain is taken in, the other is concurrently played out. As result of the spiral stack-up of these sheave chains the one being taken in increases in effective moment arm about the common mandrel axis while the moment arm of the other decreases. By connecting one chain to a downhole pump rod string and the other to a counterbalance, a configuration results in which the kinematic effects (angular and linear momentum) are continuously exchanged with the static effects (moment arm), resulting in an oscillatory system. Thus only the work expended in friction and in bringing the well fluids to the surface has to be compensated.
In the foregoing system this power input has been found to be best achieved through a reversible electric motor turned on in the proper direction once the pump was sufficiently close to the synchronous motor rate. Thus the starting current levels in the motor could be reduced and the system could be operated closer to optimum efficiency.
In my further development I have found that additional power optimisation can be had by departing from essentially sinusoidal oscillations. It is therefore one object of the present invention to provide a geometric relationship in the counterbalanced system above described which effectively shortens the periods of reversal of the oscillatory stroke.
Furthermore, I have found that by monitoring the states of the pumping system logical controls may be exercised over the motor excitation periods to insure optimal current draw and to recognize anomalies. Thus my second object is to provide a logical system herein which both controls the cycling of power and which, furthermore, compares selected measurements to recognize a failure.